This invention relates in general to a two-way AC power line communications system which utilizes the neutral and ground lines in an existing electrical power distribution network as the transmission medium. In particular, this AC power line communications system is operable to transmit data to and receive data from each room or designated area in a building or building complex over the existing AC power lines. The AC power line communications system described herein is well suited to be used in combination with a conventional room status indicating system to periodically transmit to and receive from each room or designated area of buildings such as a hotel, motel or hospital complex information which describes the status of each room in the complex, controls the operation of various equipment in each room of the complex, monitors various parameters or features of each room in the complex and initiates various service functions within each room of the complex.
In buildings such as a large hotel, motel, hospital or nursing home complex, a significant number of manhours is spent each day monitoring the status of the rooms in the complex and in performing other routine monitoring and service functions. For example in a hotel/motel complex, these routine functions include determining which of the occupied rooms have been vacated and distributing this information to the cashier, front desk and cleaning staff. Additional routine tasks which are commonly performed by the hotel/motel staff include coordinating housekeeping services to maintain a current listing of the occupied rooms, the empty rooms which have already been cleaned, and the rooms which are not available for service due to maintenance reasons. In most hotels and motels, the hotel/motel staff also performs a message-waiting service to indicate to guests that an undelivered message is waiting for them at the front desk and wake-up services for altering a guest at a particular time.
In a hospital and/or nursing home complex, a considerable amount of time is spent each day in gathering and processing room status information. The problem of monitoring patient location is another time consuming task which is routinely performed by the staff of the hospital. Another monitoring function which is typically performed by the hospital staff is that of informing the kitchen as to the number and type of the meals to be prepared. Finally, the handling and transmission of messages and other emergency information to the staff of the hospital is now manually conducted by a member of the staff.
An existing room status indicating system, which is capable of performing several of the above mentioned functions more efficiently, is given and described in the patent to Kabat et al., U.S. Pat. No. 3,810,096, issued May 7, 1974, which is incorporated by reference herein.
This room status indicating system is capable of transmitting digitally encoded information from a remote transmitter to a central line receiver over the neutral and ground lines of the AC power distribution network in a building or building complex. The transmitter includes a retractable power cord for coupling the transmitter with the AC power distribution network and mechanical switches for physically programming data into the transmitter, the power cord is placed into any wall outlet and a "push to transmit" button on the transmitter is depressed. The transmitter data is received by the central line receiver which operates in conjunction with a special purpose computer to decode the received data and to update the information stored in the memory of the computer in response to the content of this data. This system also includes a number of peripheral data terminals which are operable to pass information to and from the special purpose computer of the system and a status display board which provides a visual indication of the status of each room. While this system presents a significant advance over the prior art, it still lacks the desirable feature of being able to conduct from a central location two-way communications with each room or designated area in the hotel, motel or hospital complex.
The two-way AC power line communications system of the present invention is compatible with the room status indicating system described in U.S. Pat. No. 3,810,096 or with a general purpose computer to provide an improved room status indicating system which is capable of not only receiving data central location information from a remote transmitter but also of selectively transmitting from the central location information to a remote transceiver placed in each room or designated area of the building complex.
The two-way AC power line communications system of the present invention is basically comprised of a central processing unit and a plurality of room control units which are placed in each room or designated area in the building complex. The central processing unit acts as a central information depository and is provided with a memory unit for storing a room list and data pertaining to each room on the list. The central processing unit is also capable of selectively communicating with each room control unit and of processing the data received from these room control units. The central processing unit initiates communication with a particular room control unit by generating and transmitting over the power distribution network an address code corresponding to the unit to be contacted. The central processing unit is also capable of receiving information from peripheral data terminals associated with the system and of providing data to a particular data terminal in response to a request for information from that terminal. Finally, the central processing unit is electrically coupled with a status display board to initiate display of the stored data pertaining to each room of the complex.
The room control units, on the other hand, act as transceivers which are capable of carrying on two-way communications with the central processing unit over the AC power lines associated with the building or the building complex. Each room control unit is equipped with circuitry for receiving from the central processing unit an interrogation signal comprised of an address and data code. The room control units are also equipped with circuitry for comparing the address portion of the received interrogation signal with a preselected address code programmed into the unit. A room control unit responds to the reception of an interrogation signal having an address code representative of that room control unit by transmitting to the central processing unit a return signal containing data accumulated by the room control unit from external sources and data previously provided to the room control unit from the central processing unit.
Placement of a room control unit in each room of a hotel, motel or hospital complex creates a number of operating problems not encountered in the prior art. The large number of room control units requires that data from the room control units be provided to the central processing unit in an orderly and disciplined manner. If the room control units were allowed to transmit data to the central processing unit in a random manner, it is highly probable, given the large number of room control units, that two or more of these units would be transmitting data simultaneously. The simultaneous transmission of data by two or more room control units would impede the proper operation of the system because these signals would interfere with each other making all of the data received by the central processing unit completely unintelligible. To overcome this problem, the AC power line communications system of the present invention sequentially polls each of the room control units. In other words, the central processing unit contacts and receives data from each of the room control units sequentially to prevent two room control units from simultaneously transmitting data to the central processing unit.
The placement of a plurality of room control units on a single communications line also presents a line loading and/or "suck-out" problem which is not present in the prior art because conventional room status indicating systems only engage in one-way communication. Each of the room control units of the present invention acts as a receiver which dissipates a portion of the transmitted signal. The amount by which the transmitted signal is dissipated is directly related to the number of room control units connected to the communications line. For example, as the number of room control units increases, the amount of signal dissipation increases proportionally. If this loading problem (and/or suck-out) is not properly controlled, the strength of the transmitted signal may be dissipated to the point where the receiving unit is not capable of recognizing the signal. It has been found, that signal dissipation can be significantly reduced by providing each room control unit with a high input impedance. The room control unit, however, should be coupled with the AC power line by means of a low impedance whenever it is transmitting. To fulfill both of these operating requirements, the room control unit includes a unique transmitter which is coupled with the neutral line of the power distribution network through one of a three branch coupling network. The second branch of this network is connected directly to the neutral line of the AC distribution network while the third branch of this network is electrically coupled with the receiver of the room control unit through a high impedance circuit element and a filter and amplifier network. The subject invention is capable of reliably transmitting and receiving digital information even though an excess of 50 or more rooms or areas (locations of the room central unit) be used.
The transmitter is comprised of a tri-state switching device which is comprised of two switching transistors and associated control logic. These switching transistors are arranged to present a high input impedance if the transmitter is not transmitting and to provide a low impedance whenever the transmitter is transmitting. In particular, these transistors are maintained in a cut-off state if the transmitter is not active and are capable of alternately connecting their branch of the three branch coupling network to one or two different sources of voltage in response to an alternating control signal provided to the base terminal of these transistors from the transmitter logic. Through this switching action, the tri-state switching device is capable of introducing a large level signal onto the AC neutral line which acts as a frequency modulator. As a result, this device is capable of assuming one of three different operating states in response to other control signal from the transmitter logic. These three operating states include a high voltage state, a lower voltage state, and a cut-off state wherein the tri-state switching device introduces a high input impedance between the AC neutral line and the transmitter of the room control unit.
The nature of the operating environment and the functions being controlled by this system require that an error-type checking routine be incorporated into the design of the system to ensure that the control functions are properly activated upon command and are not inadvertently activated by a noisy signal. During the polling sequence performed by the system, the central processing unit transmits an interrogation signal comprised of an address code. Upon receiving an interrogation signal containing its address code, a room control unit transmits to the central processing unit a return signal consisting of data previously received by the room control unit from the central processing unit and the data accumulated by the room control unit from external sources. Upon receiving this return signal, the central processing unit compares the received data with the data stored within its associated memory. If the receiver data coincides with the stored data, the central processing unit continues its polling operation by contacting another room control unit. A discrepancy, however, causes the central processing unit to poll that room control unit for a second time.
Upon receiving a second return signal from the same room control unit, the central processing unit compares the data contained in this signal with the data stored in its associated memory. If this data coincides, the central processing unit assumes that the difference between the stored data and the data received during the first return signal was caused by noise on the communication line. The central processing unit then continues its polling operation by contacting the next room control unit. A discrepancy however, between the data contained in the second return signal and the stored data causes the central processing unit to compare the data contained in the second return signal with the data transmitted to the central processing unit by the first return signal. If this data coincides, the central processing unit assumes that the difference between the stored data and the data received within the first and secnd return signals is the result of new information rather than noise on the communications line. The central processing unit then makes a rigid comparison between the data contained within the first and second return signals and the data stored in its associated memory to determine where the difference lies.
If the above difference resides in the data accumulated by the room control unit from the external sources, the data stored within the memory associated with the central processing unit is simply updated and the polling operation of the central processing unit is continued. If, on the other hand, the difference in the stored and received data resides in the data initially transferred by the central processing unit to the room control unit, the central processing unit addresses this room control unit for a third time. Upon being contacted by the central processing unit for the third time, the room control unit is placed in condition to receive new data from the central processing unit. After the room control unit enters this condition, the central processing unit contacts the room control unit for a fourth time. The room control unit responds to this fourth transmission by returning the newly received data to the central processing unit. The central processing unit then compares this data with the data stored within its memory. If the received data coincides with the stored data, the central processing unit contacts the room control unit for a final time. The room control unit responds to this transmission by causing the data received during the fourth transmission to be stored in a storage register associated with this room control unit. The room control also transmits a return signal to the central processing unit. This return signal is comprised of the newly stored data from the central processing unit and of the data accumulated by the room control unit from the various external sources. The central processing unit uses this fifth return signal to confirm reception and storage of the new data within the room control unit. Upon making this determination, the central processing unit continues to the next room on its list. In this way, the AC power line communications system of the present invention incorporates an error-type checking routine which ensures that the data stored within the room control unit coincides with the data stored within the memory associated with central processing unit.
The central processing unit is also operable to monitor the operating condition of each room control unit. If a room control unit continuously responds with incorrect data or does not respond at all, the central processing unit indicates that this room control unit is out of order and continues on with its polling sequence.
The unique two-way communications feature of this AC power line communications system adds several new operating features to the conventional room status indicating system described in the U.S. patent to Kabat et al., Ser. No. 3,810,096. The AC power lines communication system of the present invention is capable of selectively transmitting an interrogation signal composed of eight independent bits of information to each of the room control units and of receiving from each room control unit an eight bit return signal composed of four independent bits of information pertaining to data accumulated by the unit from external sources and four bits of information pertaining to data stored in the room control unit in response to data previously transmitted to the room control unit by the central processing unit. As a result, a conventional room status indicating system incorporating this AC power line communications system is capable of performing not only all of the functions normally associated with room status indicating systems but also several new functions which were previously unavailable. In particular, this system is capable of gathering within a central processing unit status information from each of the room control units and of providing information to each of the room control units from the central processing unit in response to information introduced into the system at the peripheral data terminals. It is contemplated that two of the eight bits of the return signal from the room control units will be utilized to represent the status of the room. For example, one of these bits is to be used to indicate that the room has been cleaned as a stay-over while the other bit is to be used to indicate that the room has been cleaned as an occupied room. Another of the information bits in the return signal is to be used to monitor the condition of a smoke detector located in the room. Activation of the smoke detector in response to a fire causes the data bit corresponding to this feature to assume a state representative of an alarm condition. Upon becoming aware of this alarm condition, the central processing unit activates a light on a display board next to the number of the room indicating to the hotel staff that the smoke detector in that room has been activated. The fourth bit of information is to be used to represent some sort of activity which is capable of producing a switch closure type of action. Some of the activities presently contemplated include activation of an in-room movie or a pay TV program. The other four bits of the return signal comprise information previously provided to the room control unit from the control processing unit.
Some of the new operating features which are made possible by the two-way communications feature of this invention include the ability to remotely control the operation of the heating and air conditioning equipment in a particular room, the ability to convey message-waiting information to an indicator in the room and the ability to provide an automatic wake-up system operable to alert the guest in a particular room at a preselected time.
It is therefore an object of the present invention to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex.
A further object of the present invention to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines within a building or building complex wherein the system is capable of being quickly and efficiently installed in schools, hotels, motels, hospitals, office buildings and apartment complexes because it utilizes the existing power lines within the building or building complex as the communication link between the central processing unit and all of the room control units.
Another object of the present invention is to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room (or point) control units tover the AC power lines in a building or building complex wherein the central processing unit is capable of sequentially polling each room control unit of the system to thereby provide and receive information from each room control unit in a disciplined and orderly manner.
A further object of the present invention is to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room (or point) control units over the neutral and ground lines of the AC power distribution network in a building or building complex.
An additional object of the present invention is to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room (or point) control units over the AC power lines in a building or building complex wherein each room control unit is arranged to respond to a particular address code by first accepting digital data from the central processing unit and then transmitting digital data back to the central processing unit.
Another object of the present invention is to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex wherein each room control unit is arranged to present a high input impedance to the transmitted signal to thereby lessen the line loading and/or "suck-out" effect produced by the placement of a plurality of room control units on the same communications line.
An additional object of the present invention is to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex wherein the transmitter of each room control unit is comprised of a tri-state switching device which is capable of presenting a high impedance to the neutral line of the distribution network when the transmitter is not transmitting and of providing a low impedance whenever the transmitter is active.
It is a further object of the present invention to provide an AC power line communication system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex wherein the system is compatible with a room status indicating system to perform various operating or service functions within each room of a hotel, motel, schools or hospital complex and to monitor the status or condition of each of these rooms.
It is a further object of the present invention to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex wherein the system is compatible with a room status indicating system to monitor the status of each room in a hotel, motel or hospital complex in order to coordinate the housekeeping activities conducted by the hotel, motel or hospital staff and to provide an up-to-date record of the status of each room.
It is another object of the present invention to provide an AC power line communication system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units wherein the system is compatible with a room status indicating system to perform an energy conserving function by remotely controlling the operation of the heating and cooling equipment within each room of a hotel, schools, motel or hospital complex.
It is an additional object of the present to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power line in a building or building complex wherein the system is compatible with room status indicating system to activate a message-waiting indicator within a particular room of a hotel, motel or hospital complex when the guest occupying that room has an undelivered message at the front desk of the hotel, motel or hospital complex.
An additional object of the present invention is to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex wherein the system is compatible with a room status indicating system to remotely monitor the condition of a smoke detector placed in each room of a hotel, motel or hospital complex and to provide a visual indication of the condition of each detector.
It is another object of the present invention to provide an AC power line communications system which is capable of conducting two-way communications between a central processing unit and a plurality of room control units over the AC power lines in a building or building complex wherein the system is compatible with a room status indicating system to selectively convey a wake-up signal to any room within the hotel, motel or hospital complex.
A further object is to provide a data rate based on the 6th harmonic of a power distribution system of a hotel, motel, schools or hospital complex, said data rate being capable of use in any AC power line communication system.
A further object is to provide, in a system of the character described, a unique device which reduces the time for polling rooms and/or remote control units throughout the entire system.
Other and further objects of this invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.